Electromagnetic locking mechanism for a microwave oven

ABSTRACT

In a high frequency heating apparatus comprising a cabinet defining a heating chamber, a door for closing the heating chamber, a high frequency oscillator, and a timer for presetting the operating time of the oscillator, there are provided an electromagnetic locking mechanism which is energized together with the timer for locking the door in the closed position. Also provided is a switch operated by the locking mechanism for controlling the operation of the high frequency oscillator to deenergize the high frequency oscillator when the door is unlocked.

United States Patent 1191 Asanuma 1 Jan. 8, 1974 [5 ELECTROMAGNETICLOCKING 3,480,753 11/1969 Wilson et a1 219/1055 MI R WAVE OVEN 3,196,2427/1965 De Vries et al 219/1055 MECHANISM R A C 0 2,674,}14 4/1965Uberbacher.... 70/281 X [75] Inventor: Kazuyoshi Asanuma, Yoko 3,125,3653/1964 Eigelbach 292 7 Japan [73] Assigneez Tokyo Shibaura Electric Co.,Ltd., p i Ex i -J, V, Truhe KaWaSaki-Shi, JaPaII Assistant ExaminerHughD. Jaeger [22 Filed: p 14 1971 Attorney-Flynn & Frishauf [21] Appl. No.:133,840 I 571 I ABSTRACT 30 F Al't' P"tDt 1 orelgn pplca Ion "on y a ina h1gh frequency heatlng apparatus comprismg a [970 Japan 45/37606 f fmodel) cabinet defining a heating chamber, a door for closing 1970 Japan45/3760? (ut'my model) the heating chamber, a high frequency oscillator,and g a timer for presetting the operating time of the oscilla- Z F'219/1055 70/ tor, there are provided an electromagnetic locking 'i i 393396 mechanism which is energized together with the timer 1 W 3 3: 2 4 6f for locking the door in the closed position. Also provided is a switchoperated by the locking mechanism for controlling the operation of thehigh frequency oscillator to deenergize the high frequency oscillator[56] References Cited when the door is unlocked.

UNITED STATES PATENTS 3,659,068 4/1972 Duffner et a1. 219/1055 8 Claims,4 Drawing Figures 1 ELECTROMAGNETIC LOCKING MECHANISM FOR A MICROWAVEOVEN BACKGROUND OF THE INVENTION This invention relates to a highfrequency heating apparatus for heating various objects by utilizinghigh frequency electromagnetic waves of 2,450 MHz, for example, and moreparticularly to a high frequency heating apparatus including an improveddevice for prethe high frequency electromagcillator for radiating thehigh frequency electromagnetic wave in the cooking chamber and a doorfor closing the cooking chamber. Should the door fails to completelyclose the cooking chamber, the electromagnetic wave would leak outwardlythrough a small gap between the door and the cabinet thus adverselyaffecting nearby communication apparatus, a television receiver forexample, and a human body. Accordingly, it is highly desirable todeenergize the magnetron oscillator whenever the door is opened. To thisend, it has been the practice to use an electric switch so interlockedwith the door that it deenergizes the magnetron oscillator. Such aswitch, however, cannot be operated quickly because'of its inherent timelag in the opening of its contacts and the mechanical lost motion ofthemechanism interlocking the switch and the door. Thus, inadvertentopening of the door causes leakage of the electromagnetic waves duringan interval between initiation of-the opening of the door and the actualopening ofthe switch. Should the switch fail to interrupt'the circuitdue to welding of the'contacts thereof, for exam ple, a large quantityof the electro-magnetic waves would leak out.

" It is a'n'object of this invention to provide a high frequency heatingapparatus provided with an improved locking device forpositivelypreventing leakage of the electromagnetic waves by locking thedoor in the closed position whenever the high frequency oscillator isoperating.

SUMMARY OF THE INVENTION controlling the operation of the high frequencyoscillator, and means for actuating the switch in accordance with theoperation of the locking mechanism thereby to stop the operation of thehigh frequency oscillator when the locking mechanism unlocks the door.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a side elevation of anelectronic oven embodying the invention;

FIG. 2 is an enlarged partial sectional view of the electronic ovenshown in FIG. 1;

FIG. 3 shows an electric circuit of the electronic oven shown in FIGS.land 2; and

FIG. 4 is an enlarged sectional view similar 2 of a modified embodimentof this invention.

Throughout the drawings like parts are designated by the same referencenumerals.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The electronic oven shown inFIGS. 1 and 2 comprises a cabinet 1 defining therein a heating orcooking chamber 2 having an access opening on one side, a magnetron 3and a stirrer fan 4 on the upper portion of the cooking chamber, thestirrer fan 4 serving to randomly distribute the electromagnetic wavesradiated by magnetron 3 throughout the cooking chamber to uniformly cookthe foodstuff loaded therein. To close the access opening, a door 5having a handle 20 is pivotally mounted on the cabinetl by means ofahinge 6 located at the lower edge of the access opening. Spaced apartfirst and second door switches 7a and 7b are disposed in the spacebetween the side walls of heating chamber 2 and cabinet 1. To actuatethese door switches first and second door switch operating levers 8a and8b are pivotally connected to the door at their one ends to extend intothe cabinet through slots, now shown, in the front wall 1a of thecabinet. The inner ends of the switch operating levers 8a and 8b arebiased upwardly by means of springs 9a and 9b connected between theselevers and the side wall of the cabinet, thus closing door switches 7aand 7b when the door is closed. As the door is opened, the inner ends ofthe levers 8a and 8b disengage the operating levers of the door switchesthus opening the same. A hollow panel board 10 provided to FIG.

with a timer 30 and another control member is.

mounted on the upper portion of the front wall 10.

As best shown in FIGQZ, a locking mechanism 11 comprising anelectromagnetic coil 12 and an armature or locking rod 13 freelyextending through the electromagnetic coil is housed in the hollow panelboard 10. The locking rod 13 is normally biased upwardly by means of aspring 14 interposed between a flange 13a on the upper end of rod 13 andthe upper surface of coil 12. A micro-switch 16 is mounted in thecabinet 1. The operating lever 16a of the micro-switch extends into theupper portion of panel board 10 through an opening 17 formed in thefront wall la of the cabinet and the rear wall 10a of the panel board.Thus, when the electromagnetic coil 12 is deenergized the rod 13 ismoved upwardly by spring 14 to open micro-switch 16. Concurrentlytherewith, the lower end of locking rod 13 is positioned in an opening18 in the lower wall 10b of the panel board 10. Upon energization ofelectromagnetic coil 12, the locking rod 13 is pulled downwardly againstthe action of spring 14 to protrude into an opening 19 in the upper sidewall 5a of door 5, thus locking the same to the cabinet 1. At the sametime, op-

mary winding 24a connected across an AC. source 21 through fuses 22 and23, normal open contacts 32a and 32b of an electromagnetic contactor 32and first door switch 7a. The secondary winding 24b of transformer 24 isconnected across the anode electrodes and the cathode electrode of amagnetron oscillator 3 through a rectifier circuit 25 comprising a diodeD and a capacitor C. Across the junctures between fuses 22 and 23 andcontacts 32a and 32b is connected a lamp 27 through a' source switch 27.Further, in parallel with lamp 27 is connected the primary winding 28aof a low voltage transformer 28, secondary winding 28b thereof beingconnected across the cathode heater of magnetron 3. One terminal ofsecondary winding 28b is connected to the juncture between diode D andcapacitor C of the rectifier circuit. A series circuit including athermal switch 29 responsive to an excessive temperature rise ofmagnetron 3, an operating motor 30M of a timer 30 for setting theoperating time of the magnetron, the time delay contact 30a of the timerand the third normal open contact 32c of electromagnetic contactor 32 isconnected in parallel with lamp 27. A motor 31 for driving stirrer fan 4and the electromagnetic coil 12 are connected in parallel with timermotor 30M through contact 320. A series circuit including the coil ofelectromagnetic contactor 32, the fourth normal open contact 32d and themicro-switch 16 is connected in parallel with stirrer fan motor 31. Acooking switch 33 is connected in parallel with the fourth normal opencontact 32d.

Upon closure of switch 26, the cathode heater of magnetron 3 isenergized through low voltage transformer 28 to preheat the cathodeelectrode. After load ing a foodstuff to be cooked in the cookingchamber 2, door is closed to close door switches 7a and 7b. When thetimer 30 is set to a predetermined time, its contact 30a is closed toenergize the electromagnetic coil 12 and stirrer fan motor 31. Thus, thelocking rod 13 is pulled downwardly into opening 19, locking the door 5to cabinet 1 concurrently with the setting of timer 30. At the sametime, the operating lever 16a is released from the locking rod 13 toclose micro-switch l6. Then,cooking switch 33 is closed to energizeelectromagnetic contactor 32 thus closing its normal open contacts 32a,32b, 32c and 32d. Closure of contact 32d establishes a self holdingcircuit for the electromagnetic contactor around cooking switch 33.Closure of the third contact 32c energizes timer motor 30M to start itsoperation. On the'other hand, closure of the first and second contacts32a and 32b energizes the high voltage transformer from source 21 andthe output of the high voltage transformer is applied to magnetron 3 viarectifier circuit 25. Thus, magnetron 3 initiates oscillation to supplythe high frequency electromagnetic waves to the cooking chamber to cookthe foodstuff therein. After elapse of the preset time of timer 30, itstime delay contact 30a is opened to denergize timer motor 30M andelectromagnetic contactor 32, thus opening its contacts 32a, 32b, 32cand 32d whereupon magnetron 3 is denergized to stop oscillation. Openingof time delay contact 30a also denergizes electromagnetic coil 12 torestore locking rod 13 thus unlocking door 5.

In this manner, as the door is positively locked in its closed positionwhile magnetron 3 is operating thus effectively preventing inadvertentopening of the door. Where it is necessary to open the door duringcooking it is necessary to open source switch 26 or to manually returntimer 30 to the zero'position for unlocking the door. In this manner,whenever the door is brought to the openable condition, the magnetron isalways deenergized to solve the problem of the leakage of theelectromagnetic waves. Should the door 5 not be positively locked, forexample where locking rod 13 is not fully inserted into opening 19 ofdoor 5, micro-switch 16 will be held in the opened condition so thatclosure of cooking switch 33 is not effective to energizeelectromagnetic contactor 32. In such a case, of course the magnetronisnever energized. Thus, there is no danger of the leakage of theelectromagnetic waves caused by improper locking operation. 1 V

In a modified embodiment of this invention shown in FIG. 4, anelectromagnetic coil 40 is secured to the inside of cabinet 1 by meansof a support 41. An armature 42 operated by the coil 40 has its upperend connected to a lever 43 with one end pivotally connected tocabinet 1. The lever 43 extends through opening 17 into hollow panelboard 10 and is normally biased in the counterclockwise direction by aspring 44. The outer end of lever 43 is connected to the upper end of alocking rod 45 through a pin and slot connections 46 and 47. Whenelectromagnetic coil 40 is not energized, the locking rod 45 is held inits upper position by the action of spring 44 wherein the lower end oflocking rod 45 is positioned in opening 18 through the lower wall 10b ofthe panel board 10. Under these conditions, the upper end of rod 45engages the operating button 16b of micro-switch 16 to open the same.Energization of the electromagnetic coil 40 drives locking rod 45downwardly against the force of spring 44 thus insert- I ing rod 45 intoopening 19 of door 5 whereby the door is locked. Lowering of rod 45releases the operating button 16b thus closing micro-switch 16. Similarto the first embodiment, the electromagnetic coil 40 is connected to beenergized when timer 30 (FIG. 3) is set. When the coil is energized,armature 42, lever 43 and locking rod 45 are moved to positionsindicated by dotted lines. After a predetermined time, that is after theelapse of the set time of the timer, electromagnetic coil 40 isdeenergized to open micro-switch l6 and to unlock door 5. F

What is claimed is: 1. In a high frequency heating apparatus comprisinga cabinet defining therein a heating chamber with an access opening, adoor for closing said access opening, a high frequency oscillator forradiating high frequency electromagnetic waves in said heating chamber,and a timer for presetting the operating time of said high frequencyoscillator, 1

the improvement which comprises: an electromagnetic locking mechanismmounted on said cabinet, said locking mechanism being energized togetherwith said timer for locking said door to said cabinet, a switch disposedin said cabinet for controlling the operation of said high frequencyoscillator, and means operatively coupled to said locking mechanism foractuating said switch in accordance with the operation of said lockingmechanism such that operation of said high frequency oscillator isdisabled when said locking mechanism unlocks said door and is enabledonly when said locking mechanism locks said door.

2. The high frequency heating apparatus according to claim 1 whereinsaid locking mechanism comprises a coil and a spring biased locking rodoperated by said coil to engage and disengage a locking rod receivingopening in said door.

3. The high frequency heating apparatus according to claim 1 whereinsaid locking mechanism comprises an electric coil disposed in saidcabinet, an armature driven by said coil, an independent locking rodcooperating with a locking rod receiving opening in said door and withsaid switch, and a lever operatively interconnecting said armature andsaid locking rod.

4. The high frequency heating apparatus according to claim 1 whereinsaid heating apparatus further includes a hollow panel board mounted onsaid cabinet adjacent said door and said electromagnetic lockingmechanism is positioned in said panel board.

5. The high frequency heating apparatus according to claim 3 whereinsaid lever is a spring biased lever.

6. The high frequency heating apparatus according to claim 5 whereinsaid lever is spring biased in such a direction as to normally maintainsaid high frequency oscillator disabled when said electromagneticblocking mechanism, is not operated.

7. The high frequency heating apparatus according to claim 2 whereinsaid means for actuating said switch includes a lever operativelyinterconnecting said blocking rod and said switch. I

8. The high frequency heating apparatus according to claim 7 whereinsaid lever is spring biased.

1. In a high frequency heating apparatus comprising a cabinet definingtherein a heating chamber with an access opening, a door for closingsaid access opening, a high frequency oscillator for radiating highfrequency electromagnetic waves in said heating chamber, and a timer forpresetting the operating time of said high frequency oscillator, theimprovement which comprises: an electromagnetic locking mechanismmounted on said cabinet, said locking mechanism being energized togetherwith said timer for locking said door to said cabinet, a switch disposedin said cabinet for controlling the operation of said high frequencyoscillator, and means operatively coupled to said locking mechanism foractuating said switch in accordance with the operation of said lockingmechanism such that operation of said high frequency oscillator isdisabled when said locking mechanism unlocks said door and is enabledonly when said locking mechanism locks said door.
 2. The high frequencyheating apparatus according to claim 1 wherein said locking mechanismcomprises a coil and a spring biased locking rod operated by said coilto engage and disengage a locking rod receiving opening in said door. 3.The high frequency heating apparatus according to claim 1 wherein saidlocking mechanism comprises an electric coil disposed in said cabinet,an armature driven by said coil, an independent locking rod cooperatingwith a locking rod receiving opening in said door and with said switch,and a lever operatively interconnecting said armature and said lockingrod.
 4. The high frequency heating apparatus according to claim 1wherein said heating apparatus further includes a hollow panel boardmounted on said cabinet adjacent said door and said electromagneticlocking mechanism is positioned in said panel board.
 5. The highfrequency heating apparatus according to claim 3 wherein said lever is aspring biased lever.
 6. The high frequency heating apparatus accordingto claim 5 wherein said lever is spring biased in such a direction as tonormally maintain said high frequency oscillator disabled when saidelecTromagnetic blocking mechanism is not operated.
 7. The highfrequency heating apparatus according to claim 2 wherein said means foractuating said switch includes a lever operatively interconnecting saidblocking rod and said switch.
 8. The high frequency heating apparatusaccording to claim 7 wherein said lever is spring biased.